I am the facility manager of a very large commercial space which has a telecommunications cable chase and an attic type space between the top (3rd) floor and the roof.  The building has an AHU which supplies conditioned air to the hallways which is separate from the conditioned air to the workspaces.  The hallway AHU also has OA ventilation incorporated.  In addition to supplying conditioned & OA to the hallways the hallway AHU supplies a fixed amount of air to the attic area above the 3rd floor and a fixed amount of air to the IT cable chase.  Calculations off the building drawings say that 10,000 cfm is supplied to the attic area and about 9,000 cfm is returned (although we cannot figure out where the 1,000 cfm could possibly go).  For the IT cable chase we are supplying about 8,000 cfm of air of which all of this air is exhausted to the outside.

The question - do I need to be supplying this volume of air to the attic and cable chase areas?  They are both unoocupied.  Can the outside air be removed and supply only building air?  Is the volume way too high and could I reduce the amount of air supplied or even eliminate completely.  I am conditioning thousands of cfm or outside air and then sending it up an exhaust stack.  There has got to be a better way.....   Rick